Ets proteins comprise a large, conserved family of transcription factors that regulate the expression of genes involved in growth control, cell differentiation, and development. Over 30 Ets proteins have been identified in higher eukaryotes ranging from the fruit fly Drosophila melanogaster to humans. Ets proteins are defined by a unique DNA-binding domain, called the Ets domain, which is structurally and functionally distinct from DNA-binding domains in other transcription factors. Ets proteins are encoded by proto-oncogenes which, when misregulated, contribute to the development and progression of neoplastic diseases. (See reviews by MacLeod, K. et al. (1992) Trends Biochem. Sci. 17:251-256; Seth, A. et al. (1992) Cell Growth Differ. 3:327-334; and Wasylyk, B. et al. (1993) Eur. J. Biochem. 211:7-18.)
The founding member of the ets gene family is the v-ets oncogene from the acutely transforming avian retrovirus, E26, which causes erythroid and myeloid leukemia in chickens. v-ets (E26 transformation-specific) is derived from the c-ets-1 proto-oncogene, which is normally present in the chicken genome. Integration of this proto-oncogene into the viral genome resulted in the formation of an oncogenic fusion gene containing v-ets. Since the discovery of v-ets and its progenitor, c-ets-1, many ets-related proto-oncogenes have been characterized in diverse species, with up to several divergent ets genes present in a single species. These divergent genes appear to have been generated by multiple gene duplication events involving a single ancestral ets gene.
All Ets proteins contain a characteristic Ets domain, which is necessary and sufficient for DNA binding. This domain encompasses about 85 amino acids located in the C-terminal region of the protein. The C-terminal portion of this domain is enriched in basic amino acid residues that may directly interact with DNA. The Ets domain also contains three diagnostic tryptophan residues, spaced about 17 to 19 amino acids apart, and a nuclear localization signal. Structural analyses predict that regions of the Ets domain surrounding the first and third tryptophans are a-helical. The Ets domain can bind to DNA as a monomer, unlike other DNA-binding domains which require oligomerization for DNA-binding activity. In addition, some Ets proteins also contain an N-terminal helix-loop-helix domain, which may be involved in protein-protein interactions. This domain, together with the remainder of the protein, is conserved weakly among Ets proteins.
The Ets domain binds to a 10-nucleotide motif with an invariant purine trinucleotide core. Variations in the nucleotides flanking the core may contribute to the specificity of Ets binding. The Ets-binding motif has been identified in both the 5′ and 3′ regulatory regions of a variety of genes, many of which are involved in T-cell differentiation and proliferation. Such genes include, for example, those encoding T-cell receptors, cytokines, hematopoietic growth factors, and other proteins involved in T-cell signaling. In addition, some proto-oncogenes such as fos and the ets genes themselves contain Ets-binding motifs in their promoters. Interestingly, Ets-binding motifs are also present in the regulatory regions of some viral genomes, including those of human immunodeficiency virus-1 and Epstein-Barr virus.
ets gene expression is responsive to mitogens that trigger Ras-, calcium-, and protein kinase C-mediated signal transduction pathways. In addition, Ets protein activity is regulated by post-translational modifications and protein-protein interactions. For example, two human Ets proteins, ETS1 and ETS2, are inactivated by phosphorylation in differentiated T-cells. Moreover, the interaction of ETS1 and ETS2 with other transcription factors, such as Fos and Jun, determines their DNA-binding specificity and level of activity. (Basuyaux, J. P. et al. (1997) J. Biol. Chem. 272:26188-26195.)
Ets proteins are important for various developmental processes. In Drosophila, seven different Ets proteins are expressed at various times during development. One of these proteins, E74A, is specifically involved in the metamorphosis from larva to adult. Another protein, Yan/Pok, plays a role in the formation of photoreceptor cells in the developing eye. A third protein, encoded by D-ets-4, is expressed in pole cells, which ultimately give rise to the adult germline, during a restricted time period of early embryonic development. (Chen, T. et al. (1992) Dev. Biol. 151:176-191.) In mice, the ets gene, TEL, is essential for normal development. Homozygous deletion of TEL is lethal during early embryogenesis. Blood vessel formation is defective in the extra-embryonic yolk sac, and neural and mesenchymal cells undergo apoptosis within the embryo. (Wang, L. C. et al. (1997) EMBO 16:4374-4383; Golub, T. et al. (1994) Cell 77:307-316.) In addition, human ETS1 and ETS2 appear to play a distinct role in T-cell maturation in the fetal thymus.
The conversion of ets proto-oncogenes to oncogenes with transforming activity can be achieved by three basic mechanisms: overexpression, proviral integration, or chromosomal translocation. First, overexpression of either human ETS1 or ETS2 transforms NIH3T3 mouse fibroblasts. The transformed cells induce tumors when injected into immunodeficient mice. In addition, individuals with Down's syndrome, caused by an extra copy of all or part of chromosome 21, are predisposed to develop leukemia. The ets genes ERG and ETS2 are located in the minimal region of chromosome 21 associated with Down's syndrome, suggesting that increased dosage of ERG and ETS2 contributes to leukemogenesis. (Papas, T. S. et al. (1990) Am. J. Med. Genet. Suppl. 7:251-261.) Second, virus-mediated erythroleukemia is induced in mice by integration of Friend murine leukemia provirus or spleen focus-forming provirus into the host genome adjacent to ets coding regions. The viral regulatory sequences act as enhancers of host ets expression. Third, chromosomal translocations involving ets loci have been implicated in several leukemias and lymphomas. For example, a chromosomal translocation which fuses the region of TEL encoding the Ets domain to the MN1 gene results in the expression of a chimeric transcription factor implicated in myeloid leukemias. (Buijs, A. et al. (1995) Oncogene 10:1511-1519.) ets gene activity may also contribute to the metastasis of existing tumors by promoting tumor vascularization and by stimulating the expression of enzymes that break down extracellular matrix proteins. Both of these activities allow tumor cells to migrate from the site of the primary tumor.
The discovery of a new prostate associated Ets protein and the polynucleotides encoding it satisfies a need in the art by providing new compositions which are useful in the diagnosis, treatment, and prevention of cell proliferative, immune, reproductive, and developmental disorders.